Stored Energy in Gaps: A Science Fair Project

Project Board: Where Does the Energy Hide?

1For the county science fair, eighth graders Ximena Whitfield and Haruto Sato wanted to know how energy can be stored between objects that are not touching. Their teacher reminded them that potential energy is stored in a system of objects that pull or push on each other, and that the amount depends on how the objects are arranged.

2In Test 1, they dropped a 50 g steel ball into a tray of damp play sand. They changed the drop height, measured from the bottom of the ball to the sand. After each drop they measured the depth of the crater with a thin ruler, then smoothed and pressed the sand flat with the same block of wood. They used the same ball and the same tray of sand for every drop and ran three trials at each height. Table 1 shows the average crater depth.

3In Test 2, they used two ceramic ring magnets on an upright wooden dowel. The magnets faced each other with like poles, so the top ring floated 20 mm above the bottom ring. Haruto pressed the top ring down to a smaller gap, held it still, and let go. Ximena filmed the ring against a ruler and recorded how high it jumped above its floating position. They ran three trials for each gap. Table 2 shows the averages.

4Finally, they flipped the top ring over so the two magnets attracted each other. Haruto held the top ring at different gaps above the bottom ring and let go each time. From a 5 mm gap the ring closed with a soft click. From a 15 mm gap it slammed down with a loud crack and bounced.